An integrated simulator for endolaryngeal surgery

Authors


  • The authors have no funding, financial relationships, or conflicts of interest to disclose.

Abstract

The acquisition and maintenance of skills in transoral microlaryngeal surgery requires extended practice. Effective mentoring of such single-operator procedures is not possible, making it important for trainee surgeons to acquire basic skills outside of the operating room before participating in procedures on patients. Currently available training simulators use either synthetic materials or human tissue, both of which have limitations. We have designed a hybrid simulator that incorporates a porcine larynx in to an airway training manikin, providing both accurate airway anatomy and natural tissue handling characteristics. This model allows training in the skills required for suspension laryngoscopy and the resection of laryngeal lesions. Further applications could include development of surgical techniques and instruments, and use in accreditation of training and revalidation of trained surgeons.

INTRODUCTION

Transoral microlaryngeal surgery has been in regular use for several decades, and the technique is well recognized as an effective, minimally invasive option for the treatment of benign and malignant tumors.1 Safe and efficacious application of these techniques to carefully selected patients requires appropriate training, not just for residents and fellows but also for practicing surgeons who are new to this approach. Unlike open procedures, trainees cannot be mentored effectively during minimally invasive laryngopharyngeal operations on actual patients because most procedures are single-operator dependent. It is therefore important that trainees acquire these skills outside of the operating room before participating in supervised procedures on patients. Additionally, as restrictions on training hours take effect, opportunities for acquiring skills have also become limited and vary depending on several factors, including institutional practice and surgical volume.

There is therefore a great need to produce laryngeal simulators both to practice the skills required for this surgery and also for the purposes of certification of practicing surgeons. A recent head and neck surgery consensus group statement from the United Kingdom recommended that surgeons performing endoscopic resection of laryngeal cancer should attend training courses that involve simulation of laryngeal dissection.2 Endolaryngeal surgical simulators using human cadaveric tissue and synthetic laryngeal models have been described.3–7 Each has its own advantages and disadvantages (Table 1).

Table I. Advantages and Disadvantages of Current Endolaryngeal Simulators
 Human Cadaveric ModelSynthetic Model
 AdvantagesDisadvantagesAdvantagesDisadvantages
AnatomyAccurate anatomy Accurate anatomy 
Availability Short supplyReady supply 
Handling characteristics Fixation may alter tissue handling characteristics Handling characteristics do not approximate natural tissue
Infective potential Potential for infection  
Expense ExpensiveRelatively inexpensive 
Educational planning Limited flexibility for scheduling training sessionsAllows easy scheduling of training sessions 

We describe a surgical simulator that recreates the challenge of endolaryngeal microsurgery using inexpensive, readily available animal tissue with anatomy closely resembling the human.

DESCRIPTION OF DEVICE

We have developed a hybrid simulator that integrates a porcine larynx into an existing airway training manikin. The manikin we chose was Life/form Airway Larry Airway Management Trainer Torso (Nasco Export, Fort Atkinson, WI) (Fig. 1). This model provides accurate airway anatomy and ease of access to the internal components.

Figure 1.

The Airway Larry manikin.

We chose the porcine larynx over other animal larynges due to its superior structural similarity to the human larynx.8–10 The similarities in cartilage dimension, vocal fold height, and cricothyroid joint rotation between porcine and human larynges exceeds that of deer and dogs.8 Unlike porcine larynges, the ovine larynx has been found to have a significantly elongated thyroid cartilage and lacks a well-defined ventricular fold.11 The intrinsic muscles and histological appearance of the porcine larynx are also similar to those in the human.8, 12 A further advantage of the porcine model is the ready supply from either slaughter houses or following nonsurvival porcine animal experiments. This ease of supply results in low costs, an important factor when developing a tool for surgical training. We harvested specimens from Yorkshire pigs, aged approximately 4 months, following nonsurvival experiments within our institutional animal facility. The protocol received full institutional review board approval, and the harvesting was approved by the Research Animal Resource Center. Specimens included the larynx and base of tongue as shown in Figure 2. The precise specimen resection margin can be designed to meet both training needs and the dimensions of the specimen in relation to the simulator. Specimens were then stored at −18°C. Specimens required 4 hours to defrost, and these defrosted specimens did not differ from fresh specimens in terms of their handling characteristics.

Figure 2.

The excised porcine larynx.

The manikin consists of a torso and a removable head and neck, which flexes and extends to recreate a realistic position for surgery. The mandible is mobile allowing access to the laryngopharynx via the mouth. The airway design incorporates realistic anatomy including teeth, tongue, hard and soft palate, epiglottis, larynx, esophagus, and trachea.

To create the hybrid model, the synthetic skin is reflected and the laryngotracheal structures are opened to allow access to the base of tongue (Fig. 3A). Deep to the synthetic skin, the model contains a plastic laryngopharynx that is opened laterally with scissors to allow access to the airway. Although the larynx could be resected entirely from the manikin, we found that by performing only a lateral pharyngotomy and maintaining the continuity of the plastic pharynx, this could then be used to hold the specimen securely in place. The porcine specimen is placed within the airway with the epiglottis abutting the base of tongue (Fig. 3B). Velcro is used to reapproximate the lateral pharyngotomy, thus securing the specimen. Although we encountered no problems with thermal damage to the plastic manikin, for added security the parapharyngeal space within the neck of the manikin can be packed with soaked cotton gauze to minimize fire risk. At this point the overlying skin is replaced.

Figure 3.

(A) Simulator prior to insertion of porcine larynx. (B) Simulator with specimen in place.

The manikin can be examined using standard laryngoscopy equipment. A suspension laryngoscope is introduced orally to expose the porcine larynx (Fig. 4). Laryngeal endoscopes are then used to assess the anatomy and suitability for surgical training.

Figure 4.

Examination of the simulator with suspension laryngoscopy.

We found that the anatomy of the manikin was realistic and provided a challenge similar to human laryngoscopy. The porcine larynx approximates the human larynx in size and has both true and false cord structures. The similarity of this model to the human equivalent makes it an ideal tool for teaching and particularly for practice of oncological CO2 laser resections.

DISCUSSION

Over the past decade the need to produce surgical skills centers and simulators has become increasingly important.2, 13, 14 The reduction in surgical trainees' hours has resulted in reduced surgical exposure. Heightened public awareness of medical errors and patient safety issues have further reduced trainee exposure to surgical cases. It is well recognized that optimal outcomes are dependent on high volumes of surgical cases and regular practice.15, 16 As such, the American Surgical Association has recommended the introduction of surgical skills labs and simulators to alleviate all of these issues.13

Simulators are available in many fields of medicine. The first human simulator, Resusci Anne, was produced by Laerdal (Stavanger, Norway) in the 1960s. Today, surgical simulators are available in many specialties,17–19 including skull base and sinus,20 tonsil,21 and middle ear22, 23 surgery. Within the field of laryngology, a number of simulators have been described.3–7 Dailey et al. used human cadaveric larynges within a system of stabilizing clamps.4 Amin et al. incorporated a cadaveric larynx into a specialized holder for rigid laryngoscopy, whereas Mohamed et al. combined a system of clips to stabilize a cadaveric larynx and a simulated scope to access the specimen.7 Although these techniques have the advantage of providing the most accurate anatomical match to human surgery, problems include cost, limited availability, noncompliance of tissue, and the potential for disease transmission.24 Moreover, the models do not recreate the anatomic challenges in terms of patient positioning and anatomy. Although placement of a human cadaveric larynx within an airway manikin has been described,6 it has yet to be used in the setting of rigid laryngoscopy or laser microlaryngeal surgery. Both Stasche et al.5 and Contag et al.3 describe a synthetic larynx model. These models recreate human tissue properties for use with a CO2 laser5 and for phonomicrosurgery.3 Although they have the advantage of synthetic materials that are easy to source, the characteristics of such material cannot recreate the feel of real tissue, which is critical to transferring skills from a laboratory to an operating room environment.

We describe a novel hybrid simulator that incorporates a porcine larynx into an airway manikin. The porcine larynx is a cheap and readily available source of animal tissue that approximates human tissue quality and anatomy. By incorporating an airway manikin, we have added the ability to recreate the technical challenges of suspension laryngoscopy. This model therefore allows for training in insertion of various configurations of laryngoscopes. Our practice is in head and neck oncology, and therefore our simulator was specifically designed for transoral endolaryngeal CO2 laser microsurgery and not for phonosurgery. However, in a center with adequate cases of benign laryngeal pathology, our simulator may be a useful adjunct for trainees to learn the intricate surgical skills required in phonosurgery. Further applications of our simulator could also include the development and practice of novel techniques and instruments prior to application in the operating room. The simulator could potentially be used in accreditation of training surgeons and revalidation of trained surgeons.

CONCLUSION

As the concept of surgical education evolves from the see one, do one, teach one approach of the past to a structured curriculum resulting in accreditation and revalidation in the future, simulators must be designed to allow safe development of surgical skills. We present an integrated surgical simulator for laryngeal surgery using a modified airway manikin and a porcine larynx.

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